The invention relates to a switch matrix for a transceiver of ultrasonic waves for establishing electrical connections between the electroacoustic transducer elements of the group activated at a given time within a configuration of transducer elements and the delay elements for delaying the output signals of transducer elements derived from received ultrasonic signals or the oscillator signals transmitted to the transducer elements for the excitation of ultrasonic oscillations.
A switch matrix of this kind is used preferentially in transceivers in which through appropriate electronic activation of transducer elements arrranged in rows a focusing point can be produced. The individual transducer elements during transmitting or receiving are activated over differently set delay elements in such a way that the different distances of the transducer elements to the focusing point are compensated.
Thus, during transmission the ultrasonic waves are superimposed in phase in the focusing point while in the remaining sound field they obliterate each other. In order to scan as large an area as possible, for instance in the body of a patient and, in order to improve lateral resolution during different transmit/receive periods, different groups of adjacent transducer elements are activated each time. The elements are activated at any given time in such a way that for each group a separate focusing point results. When the group of activated transducer elements is shifted continuously each time by one transducer element, the focusing points moves on a line parallel to the transducer elements.
In order to be able to activate the individual transducer elements during shifting of the transducer element groups, each time with the delay necessary for the production of a focusing point, the established connections between the transducer elements and the delay elements have to be changed each time after each shift. To establish each of the necessary connections between transducer elements and delay elements, a great number of switches arranged in the manner usual in a switch matrix are necessary.
A switch matrix of the mentioned type is known from U.S. Pat. No. 3,919,683. The known switch matrix is used in a transceiver of ultrasonic waves in which six transducer elements are activated simultaneously each time. The delay times for the first and the sixth transducer element of a group, for the second and the fifth element as well as for the third and the fourth element are the same in each case so that the resulting focusing point is located on the midperpendicular to the transducer element group activated at any given time.
A selection circuit is connected to the transducer element configuration which has on the input side a large number of selection switches each connected to a transducer element and on the output side six output lines connected to the switch matrix. During the shift of the transducer element group by one transducer element, each of the selection switches connected to the first transducer element of the group activated during the preceding step is opened and the selection switch assigned to the last transducer element of the newly to be activated group closed. Thus, during each advancement of the transducer elements only two selection switches need to be operated. The echo signals received by the transducer elements are transmitted over the six output lines to the switch matrix which connects each of the output lines with the delay elements necessary for focusing. Because of the described manner of advancing of the transducer elements, the assignment of the output lines of the selection circuit to the different delay elements has to be changed with each step. To this end, the known switch matrix has 18 switches of which, at any given time, three each are connected on the input side with each one of the six output lines of the selection circuit and each six on the output side with each one of three different delay elements. The control circuit for operating the individual switches has a large number of logic circuits, as for instance NAND gates, and many other additional electronic components, like transistors, such that the result represents overall a high degree of circuit complexity. The complexity would, furthermore, be greatly increased if, in order to achieve higher resolution, the number of the transducer elements of a group would be raised.
Relative thereto it is an object of the present invention to create a switch matrix of the aforementioned kind which does not need such complicated control circuity.